Note: You must install OpenCPN into your Applications folder where it belongs. The installers of the plugins of course expect it to be there.
Also for MacOS Mojave see CF thread http://www.cruisersforum.com/forums/f134/open-cpn-kind-of-a-mess-on-mojave-228973.html
For MacOS Catalina there are some issues, but look at this CF post http://www.cruisersforum.com/forums/f134/oesenc-does-not-download-to-plugins-on-opencpn-228875.html#post3054084
Use of your iPad with RealVNC and OpenCPN